SAN FRANCISCO, California (CNN) -- Lesbian activist Del Martin, at the forefront of the battle for same-sex marriage in California, died Wednesday in San Francisco. She was 87.

Martin's partner of 55 years, Phyllis Lyon, was by her side at the UCSF hospice, the National Center for Lesbian Rights said.

Martin and Lyon, 84, tied the knot June 16 in a ceremony officiated by San Francisco Mayor Gavin Newsom.

"Ever since I met Del 55 years ago, I could never imagine a day would come when she wouldn't be by my side. I am so lucky to have known her, loved her and been her partner in all things," Lyon said. "I also never imagined there would be a day that we would actually be able to get married.

"I am devastated, but I take some solace in knowing we were able to enjoy the ultimate rite of love and commitment before she passed."

Long before Massachusetts and then California legalized same-sex marriage, Lyon and Martin were integral parts of the early movement for lesbian and gay rights. They met in 1950 in Seattle, Washington, where they worked as editors of construction trade publications. They fell in love, moving in together on Valentine's Day 1953.

Martin fought to have the American Psychological Society declare that homosexuality is not a mental illnesses and advocated on behalf of battered women.

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In 1955, the couple founded the nation's first lesbian organization, the Daughters of Bilitis, and launched the first lesbian publication, The Ladder.

In the 1960s, they tried to get California lawmakers to introduce anti-discrimination bills and persuaded some police officers to stop harassing gays and lesbians at bars as part of a group Martin co-founded called the Council on Religion and the Homosexual.

Martin was also a founding member of several other organizations, including the Lesbian Mother's Union, the San Francisco Women's Centers and the Bay Area Women's Coalition. She and Lyon were co-founders of the first gay political group in the United States, the Alice B. Toklas Democratic Club, named for author Gertrude Stein's long-time partner.

After she and Lyon were the first lesbians to join the National Organization for Women with the couples' membership rate, Martin was the first open lesbian to be elected to NOW's board of directors. From that spot, she was instrumental in guiding the organization to pass a resolution recognizing lesbian issues as feminist issues.

Martin and Lyon were delegates to the White House Conference on Aging in 1991, named to it by Sen. Dianne Feinstein and Rep. Nancy Pelosi, both of California.

Kate Kendell, executive director of the National Center for Lesbian Rights, called Martin "a real hero."

"For all of Del's life, she was an activist and organizer even before we knew what those terms meant," Kendell said. "Her last act of public activism was her most personal: marrying the love of her life after 55 years.

"In the wake of losing her, we recognize with heightened clarity the most poignant and responsible way to honor her legacy is to preserve the right of marriage for same-sex couples, thereby providing the dignity and respect that Del and Phyllis' love deserved."

In 2003, lesbian filmmaker Joan E. Biren released "No Secret Anymore: The Times of Del Martin and Phyllis Lyon," a 57-minute documentary focusing on the couple's activism and relationship.

That year, the couple spoke to The Noe Valley Voice, a newspaper covering their San Francisco neighborhood, about the film and their drive to advance the rights of lesbians.

Lyon said she and Martin had no particular secret on how to keep a relationship going for decades.

"If we had a secret, we would have written a book and made a million dollars," Lyon told the Voice. "We love each other; we have similar interests. Our lives were very similar even before we met."

In 2004, San Francisco officials allowed gay couples in the city to wed, prompting a flood of applicants to the City Hall clerk's office. The officials chose Lyon, then 80, and Martin, then 83, to take the first vows.

The state Supreme Court voided those unions. Lyon and Martin, however, joined more than 20 other couples as plaintiffs in a lawsuit challenging the state's marriage laws.

On My 15, the California Supreme Court struck down the state's ban on same-sex marriage, paving the way for Lyon and Martin and other same-sex couples to marry in the state.

A standing-room only crowd at San Francisco's City Hall on June 16 saw Lyon and Martin, in a wheelchair, take their vows.

"This is an extraordinary moment in history," Newsom said. "I think today, marriage as an institution has been strengthened."

Del Martin identified her own legacy in 1984 when she said that her most important contribution was "being able to help make changes in the way lesbians and gay men view themselves and how the larger society views lesbians and gay men."